The purchasing of organic food will be promoted

The review will look at whether small and medium-sized producers are being given a fair chance to compete for contracts with public sector bodies such as schools, hospitals and prisons.

The investigation follows claims by, among others, Prince Charles that many publicly-funded organisations are not buying enough British produce.

The Food Minister Lord Whitty, who will officially launch the initiative at the Royal Cornwall Hospital Trust in Truro on Tuesday, said it would ensure "British producers get a fairer crack of the whip".

Lord Whitty admitted European competition law would prevent an explicit "Buy British" campaign but said the public sector had a responsibility to ensure British farmers had a "reasonable opportunity" to produce food.

He told the BBC: "There is a lower proportion of British food bought in public sector contracts than there is bought by the average consumer in the supermarket."

The review, being co-ordinated by the Department for Environment Food and Rural Affairs (Defra), will also exam issues such as environmental impact, waste, biodiversity, animal welfare, pesticide use and nutrition.

In addition, it will focus on ensuring appropriate standards for purchased food, including food production standards, like animal welfare and pesticide.

It also aims to promote healthier eating in canteens, the purchasing of organic foods, less waste, and identifying and tackling any difficulties UK producers have in meeting demand.

Lord Whitty said some farmers had been by-passed

The chairman of the UK Sustainable Development Commission, Jonathan Porritt, welcomed the announcement as an "excellent step forward".

He said: "The public sector has huge spending power, the NHS alone spends �500 million a year on food.

"That money should be used to support high environmental standards and viable livelihoods, and promote health and sustainable development."

Sir Don Curry, chairman of the independent implementation group overseeing the government's strategy for sustainable farming and foods, said the review marked a "real commercial opportunity for the farming industry".

He said government and industry must work together to ensure British producers can supply enough fresh and wholesome produce at the right price.

Last December, the Prince of Wales said the benefit to farmers would be enormous if organisations like the Army, hospitals and government departments spent their food budgets on UK produce.